In the specification of Japanese Laying-Open Patent Publication No. 52-118494 (1977), it is described that a thiadiazolo[3,2-a]pyrimidinone derivative represented by the general formula ##STR1## wherein R.sup.1 stands for an alkyl group or an aryl group; R.sup.2 stands for a hydrogen atom, a halogen atom, a nitro group, a carboalkoxy group or an alkyl group; R.sup.3 stands for an alkyl group or an aralkyl group; and Y stands for --SO-- or --SO.sub.2 --, exhibits an activity inhibiting proliferation of cancer cells and is useful as an anticancer agent.
In the specification of Japanese Laying-Open Patent Publication No. 58-177997 (1983), it is described that a thiadiazolopyrimidinone derivative represented by the general formula ##STR2## wherein R.sup.1 stands for a 1 or 2H-tetrazol-5-yl group, a carboxy group or a lower alkoxycarbonyl group; R.sup.2 stands for an aryl group or a heteroaryl group which may be substituted with an alkyl group, an alkoxy group, a hydroxy group or a halogen atom; X stands for an alkylene group, an alkenylene group, an alkynylene group or any of the above groups, to an end of which an oxygen atom, a sulfur atom or SO.sub.2 is attached; wherein each of the groups represented by X may be substituted with one or more linear or cyclic alkyl groups or with the substituent R.sup.2, and a physiologically acceptable salt thereof have excellent antiallergic activity.
As described above, there were known several thiadiazolopyrimidinone derivatives, which have a chemical structure similar to that of the compounds of the present invention. However, these are medicinals, and they do not clearly exhibit activities as pesticides.
We paid attention to the 5H-1,3,4-thiadiazolo[3,2-a]pyrimidin structure, which is the skeleton of many substances used as medicines, and we synthesized a number of derivatives thereof and studied their biological activities. As a result, we found that some specific compounds having the 5H-1,3,4-thiadiazolo[3,2-a]pyrimidin structure exhibit an excellent property as an agricultural-horticultural pesticide, and completed this invention.
That is to say, the object of this invention is to provide novel 5H-1,3,4-thiadiazolo[3,2-a]pyrimidin-5-one derivatives, useful agricultural-horticultural fungicidal compositions containing said derivatives, a process for preparing said derivatives as well as a class of novel compounds, which are the starting materials for preparation of said derivatives.